Pressure operated switch



Patented Sept. 19, 1944 PRESSURE OPERATED SWITCH Carl A. Otto, Milwaukee, Wis., assignor to Johnson Service Company, Milwaukee, Wis., a. corporation of Wisconsin Application August '7, 1943, Serial No. 497,791

2 Claims.

This invention relates to electric switches and particularly to switches of the fluid pressure perated type, in which the switch is operated by differentials between two fluid pressures each of which varies considerably under normal conditions, and either or both of which may reach quite high values under abnormal conditions.

Specifically the problem was to produce for use in controlling an oil cooler for aeronautical engines a precisely-acting small switch which would shift in response to a differential of approximately 26 p. s. 1. between two pressures, one of which normally varies between 20 and 40 p. s. i. and the other between 2 and 5 p. s. i., and either or both of which may rise to 500 p. s. i. under abnormal conditions. These particular values are significant merely as indicating the erratic pressures which a small and precise device must withstand, in a field where failure cannot be tolerated, and adjustments must be maintained.

The result was secured by using two diaphragms with means to limit their motion to a safe range, together with diaphragm reinforcements capable of withstanding the extreme pressures exerted through the diaphragms without rendering the diaphragms sluggish at low pressures and without stressing the actuated parts such as the switch. The diaphragms may be made of any suitable material. Successful use has been made of synthetic plastics of good mechanical properties. Motion-limiting parts are of hardened steel, and so formed that at the limits of motion they resist the stress in simple compression and protect all the sensitive working parts from overload.

A commercial embodiment of the invention is illustrated in the accompanying drawing, in which Figure l is a face view of the complete device with the cover removed;

Figure 2 is a longitudinal section with the cover in place;

Figure 3 is a fragmentary section on the line 3-3 of Figure 1.

In the drawing a part of the device on which the switch is mounted appears at 6. The base 1 of the switch is clamped to the face of the part 6 by four screws 8 whose heads are visible in Figure 1. A gasket 9 is used to secure a tight joint.

The recess l I in base 1 is the high pressure diaphragm chamber (20 to 40 pounds) and is overlaid by diaphragm l3. It is in communication with passage l2 formed in the base and in part 6.

Overlying the marginal portion of the diaphragm I3 is spacer ring H which is notched at its top as indicated at l5 and I6 (see Fig. 1) to (Cl. ZOO-81.5)

afiord clearance for the loading spring and for the switch-actuating lever respectively. Above ring [4 is a gasket (used to seal the passage 25 hereinafter described) overlaid .by diaphragm support IT. This sustains diaphragm i8, while above the diaphragm is cap I3 with recess 2| which serves as the low pressure diaphragm chamber (2 to 5 pounds).

There are five screws 22 which pass through the parts I3, l8, 11, I4 and I3 and are threaded into base i. There is also a screw 23 which passes through parts [4 and i3 below notch i5 and is threaded into base i. A bolt 24 with nut 25 connects the parts H, [8 and I9 above the notch 15.

A passage 26 leads to chamber 2| through parts 6, 1,14, l! and 19.

Each diaphragm carries at its center a thrust device, and since these are identical, only that for diaphragm l8 need be described. On the outer side is a large hardened steel disk 21, and on the inner side is a smaller disk 28 of the same material. These are connected through the diaphragm by a hardened steel bolt and nut collectively indicated at 29.

To load the diaphragm I3 inward (downward in Fig. 2) use is made of a generally triangular steel leaf spring 3|, positioned by the pins 30 in the fulcrum 32. This is stressed by the thrust screw 33 which may be locked in adjusted positions by the check nut 34.

A micro-switch 35 having an actuating button 35 is supported on base 1 in the inclined position clearly shown in Figure 2. The leads from the switch are three in number and are indicated at 31. Microswitch is a trade name for a switch capable of switching substantial currents and requiring only very minute motion of its actuating button 35 to actuate it. Microswitches of a Wide range of types and numbers of contacts are commercially available, and any suitable type may be used. This is of the double contact type and is used to operate a small electric motor in opposite directions.

The switch button 35 is actuated by a bell crank lever 38 fulcrumed on pivot screws 39 carried by base 1. The switch is spring biased so as to force button 35 outward. Thus the button 35 can be actuated by thrust. An adjustable thrust screw 4| i mounted in the short end of lever 38 and engages button 35. A check nut 42 is provided. Th lon end of lever 38 carries a round-ended thrust head 43 which just fills the interval between the thrust members at the centers of the two diaphragms.

The mechanism is enclosed by a cover 44.

phragms. If either chamber is subjected to excessive pressure, as may happen when an engine is started while extremely cold, the parts move phragms react oppositely on thrust; and a switch of the micro-motion type actuated by said lever, the parts being so dimensioned that the inner bosses limit inward motion of respective diaphragms to minut ranges safe for the diaphragm and for the switch, whereby overloads are absorbed by the bosses and the head on the lever without straining the lever or its fulcrum.

2. The combination of two opposed closely spaced pressure chambers; connections for subjecting said chambers to different fluid pressures,

until arrested by the chamber wall, after which the bolts 29 and the head 43 are loaded in compression, without overstressing the lever 38 or the pivots 39.

What is claimed is:

1.- The combination of two opposed closely spaced pressure chambers; connections for subjecting said chambers to diflerent fluid pressures, one of which normally is dominant; spaced flexible flat diaphragms respectively forming the proximate walls of the two chambers; thrust members, one fixed to the central portion of each diaphragm, each comprising a stifi sustaining plat seated against the outer face of its diaphragm and hard thrust bosses on each side of th diaphragm; a spring'reacting inward on that diaphragm which is subject to the dominant pressure; a motion transmitting lever having a fulcrum external to the interval between the diaphragms and having an arm extending from the fulcrum into the interval between the diaphragms and there supporting a hard reaction head upon which latter the external bosses of the two diaone of which normally is dominant; spaced flexible fiat diaphragms respectively forming the' proximate walls of the two chambers; thrust members, one fixed to the central portion of each diaphragm, each comprising a stiff sustaining plate seated against the outer face of its diaphragm and hard thrust bosses on each side of the diaphragm; a leaf spring having its free end in thrust engagement with the external boss on that diaphragm which is subject to the dominant pressure; means for adjustably stressing said spring; a motion transmittin lever having a fulcrum external to the interval between the diaphragms and having an arm extending from the fulcrum into the interval between the diaphragms and there supporting a hard reaction head upon which latter the external bosses of th two diaphragms react oppositely 0n thrust; and a switch of the micro-motion type actuated by said lever, the parts being so dimensioned that the inner bosses limit inward motion of respective diaphragms to minute ranges safe for the diaphragm and for the switch, whereby overloads are absorbed by the bosses and the head on the lever without straining the lever or its fulcrum.

CARL A. OTTO. 

